Instruments which can sense departures of their own reference frame from an inertial reference frame are of practical and commercial use in many areas, for example inertial navigation and guidance. Such departures include accelerations, by way of example. Acceleration is commonly sensed by measuring either the displacement of a proof mass in response to an inertial force, or the restoring force necessary to restore the displacement of a proof mass.
Accelerometers that use electromechanical components are known in the art. In particular, multi-axis sensors are useful for inertial sensing of motion in three dimensions. In the past, such sensors have been constructed from relatively large and expensive electromagnetic components. More recently, MEMS (microelectro-mechanical systems) sensors have been fabricated from silicon wafers, using semiconductor processing techniques such as photolithography. One advantage of microfabricated sensors is the possibility of large scale production and ensuing lower costs. Another advantage is the small size and weight of the accelerometer.
The manufacturing base for electromechanical instruments is, however, saturated and on the decline. In contrast, there is a growing manufacturing base, as well as a growing body of skilled workers, in the rapidly expanding fiberoptic communications industry. Because of the large and growing infrastructure built by the fiberoptic telecommunications industry, an inertial sensor that uses only electrooptical components, and that therefore shares many subsystems and components with the fiberoptics industry, can be built economically.
An all-optical accelerometer is not only a totally innovative concept, but also very desirable, because such an accelerometer would provide many advantages over prior art electromechanical inertial sensors. For example, unlike electromechanical accelerometers, an all-optical accelerometer would have no moving wear surfaces. Therefore, the projected lifetime of such an instrument would be much greater than the lifetime of electromechanical accelerometers, since the lifetime of an all-optical accelerometer would be limited only by the optical source lifetime. Also, because the all-optical accelerometer has no moving wear surfaces, the accelerometer may be built as a flexure-less and very linear instrument. This eliminates the need for building flexural support structures, such as suspension assemblies, into the device. Further, unlike prior art MEMS sensors, it would be possible to recalibrate an all-optical inertial sensor during the operation of the device. Further, an all-optical inertial sensor can be built as a closed loop instrument, with a high dynamic range. Finally, using integrated optics and fiber optics components, the space and energy requirements of the accelerometer can be minimized.
It is therefore an object of this invention to provide an inertial sensor that is constructed using only electrooptical components. It is another object of this invention to provide an all-optical inertial sensor that is smaller, lighter, and has a longer lifetime alternative, as compared to conventional instruments. It is another object of this invention to provide an all-optical inertial sensor that leverages the presently growing communications and electro-optics infrastructure. It is another object of this invention to provide a MEMS inertial sensor that incorporates an entirely new force mechanism for MEMS devices.